The present invention relates to the optical fiber telecommunication networks, and more particularly, to the technique of service protection and failure restoration of mixed networks comprising Synchronous Optical NETwork (SONET) rings and multiple Wavelength Division Multiplexing (WDM) point-to-point links. WDM systems carrying many independent traffic channels (8/16/32 and more) over the same fiber are currently widely deployed. These systems allow to upgrade the network capacity without using additional fiber. However, the point-to-point WDM links have no built-in mechanisms for service protection (restoration) in case of fiber or cable cut. For protection purposes, WDM links currently employ the algorithms of fiber and equipment protection acquired from SONET rings.
The conventional mixed SONET/WDM networks are not adequately protected against cable cuts. When cable is cut (working and protection fibers are broken), all SONET rings passing through the broken WDM link have to switch independently. Thus, the local failure propagated across the network causing, for the number of channels over 16, traffic perturbation on a national scale. To develop adequate protection, it was suggested by the inventor of the subject patent application in the U.S. patent application Ser. No. 08/867,346 "Method and System for Service Restoration in Optical Fiber Communication Networks" to use optical switching technology to switch WDM traffic from failed WDM link to a dedicated protection ring (DPR). The dedicated protection ring was selected from the plurality of SONET rings passing through the WDM link. Optical switches deployed at transmitting and receiving WDM nodes switched WDM traffic from working fibers of WDM link to protection fibers of the dedicated protection ring.
The rapid growth of network capacity results in significant fraction of the networks being populated by WDM links. In many cases, one SONET ring comprises several WDM links. These WDM links may be adjacent to each other and have different capacity. It was shown in the aformentioned U.S. patent application '346 that for these more complicated SONET/WDM configurations, one or more dedicated protection rings may be used. However, with the increased density of WDM links, the dedicated protection rings would overlap, and network architecture will become complicated and vague.
It is therefore desirable to provide the network architecture for protection of mixed SONET/WDM networks with adjacent and multiple WDM links equivalent to SONET ring protection and sufficient for required network reliability.